Process for the production of fuel gas low in carbon monoxide



Wilhelm Herbert. Frankfurt; am Main 3,069,249 Patented Dec. 18', 1962United States Patent Otilice PROCESS FOR THE PRODUCTION OF FUEL GAS LOWIN CARBON MONOXIDE Eschcrsheim. Hans-Wcrner Gross, Buchschlag, KreisOlienbach, and Oskar Dorschner, Bad Hamburg vor der Hqhe, Germany,assignors to Metallgesellschaft Aktlengesellschnr't A.G., a Germancorpora ion No Drawing. Filed Mar. 10, 1959, Ser. No. 798,337 Claimspriority, application Germany Mar. 18, 1958 19 Claims. (Cl. 48-197) Thisinvention relates to improved gaseous fuels applicable for industrialand residential use by both municlpal and long distance distribution,and more particularly to a process by which crude fuel gases having arelatively high content of carbon monoxide and other impurities may betreated to remove substantially all of these impurities.

By subjecting carbon-containing solid fuels such as coal to oxygen andsteam treatment under pressure, gaseous fuel products may be recoveredwhich are useful for'industrial or residential .purpos'esin areas wherenatural fuel gases are not readily available. These pressureformedgaseous fuels are particularly useful in various thermal synthesisoperations. Usually, upon reducing the undesirablecarbon dioxide presentto a content of only about 2% by scrubbing techniques, the heating valueof the resulting fuel'gas is between 3700 and 4500 kcal./m. (N.T.P.),depending on the particular solid fuel charged. t I

The carbon. monoxide content of these pressure-formed fuel gasesordinarily ranges between about '18 and 32% which is considerably higherthan that of coke-oven gas (6%) or municipal gas (l to and the densityof these gaseous (fuels), after scrubbing, is higher thanthat ofcoke-oven gas as well. This carbon monoxide content varies within saidrange of 18 to 32% depending on the quantity of steam used, in thegasformation. Generally,

the higher the rate of steam addition, the lower will be the v carbonmonoxide content.

-Nevertheless, during pressure gasilication of solid fuels,disadvantageously only a part of the steam present is actuallyconverted, the remainder merely passing through the reaction zoneunused. Moreover, where fresh steam is added to the reaction zone, thesolid fuel ash does not sinter, but accumulates as a powder insteadwhich can only be removed with difficulty from the ash sluice.Additionally, it is uneconomical and technically difiicult to produce apressure-formed gas fuel with a desirable carbon monoxide content ofless than 18%.

It is an object of the invention-to overcome the above disadvantages andto provide a process for the production of fuel gas low in carbonmonoxide and substantially free from undesired impurities.

,Other and further objects will become apparent from a study of the'within specification.

It'has been found, in accordance with the invention,

. that crude fuel gas, such as that obtained by gasification of solidfuels in the presence of oxygen and steam under pressure, having a highcontent of carbon monoxide, may be treated to remove the larger portionof the carbon monoxide and attendant impurities while utilizingotherwise unreacted steam present in the crude gases, leaving thepressure gasification reaction zone to enrich the quantity ofcombustible products in the final gas.

Accordingly, a crude fuel gas upon its exit from the pressuregasification zone is suitably cooled, for example, by waterv injectionmeans to the extent necessary to separate out high boiling hydrocarbonswhich may be present. The somewhat cooled gas which is still under thesame or perhaps slightlylowcr pressure as that which it leaves thepressure'reaction zone is then reheated to about, 250 to ratusconventionally applied at a subsequent stage in the.

, c Jo steamfpresent to carbon dioxide and hydrogen.

400 C. and conducted over a conversion catalyst wherein the unused steampresent is utilized to produce a. richer combustibles content. Theconverted gas thus obtained is thereafter cooled and purified in anyknown manner.

The process according to the invention advantageously may be carried outat temperatures which are as high as those technically attainablewithout the higher carbon monoxide content unfavorably influencing thefinal composition or the density of the final pure gas. In this way, anyunused steam present in the crude gas will be efficiently and completelyused, whereby an economy in overall steam requirements will be realized.

Specifically, in accordance with the invention, crude fuel gas, such asthat leaving the pressure gasification re action zone at a pressure ofabout 25 atmospheres and a temperature of from 40.0 to 700 C. and whichcontains to carbon monoxide with respect to dry gas as well asconsiderable amounts of unused steam, high boiling hydrocarbons anddust, may be favorably purified and enriched in combusti-bles content byfirst cooling to remove most of the thereby-separatable materials suchas high boiling hydrocarbons and dust and thereafter subjecting thecooled gases to catalytic conversion at higher temperatures.

The cooling operation may be carried out by suitable water injectioncooling means, and for greater efi'iciency and economy may employ exitwater from cooling appaprocess. This first cooling step by which thetemperature of the gas is lowered to about 200 or slightly lessseparates high boiling products and dust including tars and oil dropletsfrom the crude gas, all of which may be removed therefrorn as forexample by suitable cyclone means. Still under pressure, the crude gasmay be cooled even further to about 160 to 190, as for example, bypassage through heat exchange means to remove additional vaporoushydrocarbon impurities.

The cooled crudegas which still contains under pressure -60% by volumeof steam and other impurities is then reheated, as for example, viasuitable heat exchange means, by the hot pure gases emanating from thesubsequent conversion reaction zone, to a temperature of" from about 250to 400 C. These hot gases are then conducted over a conversion catalystin said conversion reac- 'tion zone to convert a substantial part of thecarbon monoxide prcsent with a stoichiometric quantity of the unused Inthis way, little or no steam is wasted in the overall process and thequantity of gas liquors from which water must be recovered is decreased,thereby decreasing the cost of such water recovery. 7

During the conversion step, the gas increases its temperature'by about100 due to the heat of reaction. Surprisingly, this conversion takesplace at conditions almost completely corresponding to those ofequilibrium, in spite of the impurities contained in the crude gas, suchas carbon dioxide, hydrogen sulfide, organic sulfur compounds, ammonia,hydrocyanic acid, resin forming impurities, and the like, whichare-recognized catalyst poisons.

The process of the invention gives conversion yields which are from toof the theoretical. The preponderant amount of resin formers and organicsulfur compounds are removed in the conversion zone throughhydrogenation or conversion into easily separable hydrogen sulfide. Itshould be noted that not only the scrubbed pure gas but also the oilsand petroleum fractions yielded mixture of .iron oxide and chromiumoxide. However, other less expensive materials may be advantageouslyused such as active hydrated iron oxides as used for the removal ofhydrogen sulfide from carbonisation gases, bog iron ore or similar ironoxide hydrates. All of these materials may be employed separately aswell as in mixture with each other. By suitable work-up procedures, theymay be reduced to the desired particle size, dried and without furtherpretreatment employed directlyin the process. These catalysts beforeuse, nevertheless, may be essentially increased in their activitybyheating at 300 to 350 C. with already converted gas to effectreduction, since such gas still contains about 20 to 40 g./m. (N.T.P.)of

steam.

In place of iron oxide type catalysts, metals of the 6th group of theperiodic system, particularly molybdenum and tungsten, in the formoftheir oxides and sulfides, and

'metals of the 8th group of the periodic system, such as cobalt andnickel, may be used with equally good results.- Carrier substances forthese catalyst materials include mineral products, such as alumina,silica gel, and the like. These catalysts advantageously may bereadilyconverted at lower temperatures (250300 C.) than the iron oxide typecatalysts require.

The activity of the catalyst which strongly diminishes after prolongedoperation, can be renewed once again by regeneration at normal reactiontemperature with air or oxygen containing inert gases and/or steam andsubsequent reduction with converted gas low in steam content.Conventional pressure resistant means employed for pressure gasificationof solid fuels in accordance with the invention may be used for thisregeneration step.

After leaving the conversion zone, the converted gas may be precooledthrough heat exchange means, releasing the major part of its heat to thegas entering the conversion reaction zone and its residual heat throughheat exchange means to a waste heat boiler for the production of steam.Thereafter, direct or indirect cooling means may be employed for finalcooling of the gas freed from carbon dioxide and hydrogen sulfide, asfor example, by suitable conventional scrubbing techniques. Upon drying,the purified gas may be used as a synthesis gas, or directly as anindustrial or residential gas via long range or local distribution.

The purified gas obtained in accordance with the process of theinvention normally contains only about 4 to 8% carbon monoxide and itsdensity is ordinarily below that of coke oven gas. However, if desired,for specific purposes, the gas may be made to have a higher carbonmonoxide content than 8% and a higher density as well by effecting aless complete transformation in the conversion zone or by mixingnon-converted gas with the purified converted gas.

It will be seen that the process 'in accordance with the inventionwhereby a purified gas low in carbon monoxide may be produced may bereadily adapted without dilficulty to conventional apparatus forpressure gnsification of solid fuels by merely leading the crude gasfrom the conventional apparatus through heat exchange means for coolingand thereafter heating the gas and conversion reactor means for reducingthe carbon monoxide content of the gas. These additional means areconveniently positioned adjacent the pressure gasification zone, forexample, between the waste heat steam boiler and the crude gas reactorcondensers.

The invention is further illustrated by the following examples but it isto be understood that it is not to be limited thereby.

EXAMPLE 1 Conventional Production of Fuel Gas A low coking mineral coalwas gasified under an operational pressure of 23 atmospheres pressurewith oxygen and steam. The composition of the gas, after cooling andafter scrubbing in the conventional manner was:

Crude gas scrubbed nll r cuolpure gas, ing to 25, percent:

percent 29. 7 2.0 O. 5 0.7 17.0 24.1 40. l 56. 9 10.6 15. 0 l). 9 1.3 1. 2 0

Uppzr hunting value 3.970 kenL/m. pure gas (N.'l.P.). Dunsity withreference to air 0.40

Content otorgnnlr'ally bound suliur ingJm. pure gas (N.T.P.).

Consumption of gasification agents:

For crude gas For pure gas Oxygen 0.10 mfi/mflcrude gas 0.22 mn' lln.pure gas (N. (N.T.l.). Fresh steam 0.95 kg/m. crude gas 1.33 kgJm. puregas (N.'l.P.). (N.l.P.).

EXAMPLE 2 Purified Fuel Gas Low in Carbon Monoxide Content The same coalas used in Example 1 was gasified under an operational pressure of 23atmospheres pressure according to the conventional hot passagetechnique, whereinafter a gas with a high carbon monoxide content wasproduced. The following content values were obtained:

Pure gas upon A quantity of the wet crude gas after cooling to 190 washeated to 350 and conducted over a conversion catalyst comprising amixture of iron oxide and chromium oxide. The rate of flow volume was600 l. gas/h.l. catalyst (N.T.P.).

After the cooling, the gas had the following composition:

Crude con- Scrubbod ver ion pure c0ngas. pcrverslon cont gas, percentCO- 38. 3 2.0 CZHJ 0. 4 0. 6 CO 3.0 -4. 8 H. 48. 1 7B. 3 CH1 7. 8 12 7N2. 1.0 1. 6 H S 1. 4

Upper heating value 3,850 kcaL/m. pure converslon gas (N.l.P.).Density/air 0.22. Organically bound sulfur 40 rug/m. pure conversion (N.T.P.).

gas Organically bound sulfur in the oil and 0.6%.

petroleum tractions.

Consumption of gasification agents:

For unconverted crude gas For pure gas oxygenuni 0.17 nil/m. unconverted0.22 mJ/m. pure gas -gas(N. (N.T.P.).

Fresh Steam 0.65 toil/m. unconverted 0.87 lg/m. pure gas gas( .T.P.).(N. .P.).

EXAMPLE? Purified Fuel Gas Low in Carbon Monoxide Content Afterseveralweeks of operation, deposits formed by the polymerization of thehigh-boiling unsaturatedhydrocarbons, during the heating of the crudegases to 350 in the heatexchangers, could be observed. Therefore, theconversion heater was charged with a cobalt-molybdenum oxide catalystsuch as used for the refining of petroleum and crude. gas heated only to250 C. was passed at a flow volume rate of 400 m. /h.m. catalyst(N.T.P.) over the catalyst.

The conversion of the crude gas took place in similar manner to that ofExample 2, so that a pure gas of the same composition was obtained.After operating for several months inthis way, no clogging occurred inthe heat exchanger.

- The pure gas obtained in Examples 2 and 3 has a lower CO content and alower density than coke-oven gas. The content of organically boundsulfur was lower than that of coke-oven gas by 73%, that of the oil andpetroleum fractionsin Example 2 by 60% and in Example 3 by 71%. Thesteam consumption for gas low in carbon monoxide, which is obtained inaccordance-with the process of the invention, is lower by 0.46 leg/m.(N.T.P.), corresponding to 34%, than for a conventionally producedgas'which contains about five times as much 'car-' bon monoxide.

EXAMPLE 4 Catalyst Regeneration out with steam. Thereupon, the reactorwas connected in a circulation system containing a gas blast apparatusand a gas heater. The entire system was filled with an inert gas mixturemade up of a combustion gas consist.-

ing of nitrogen and carbon dioxide. This gas was conducted under normalpressure through the reactor and heated to 300; The rate of flow volumeamounted to 150 to 200 m. /h.m. catalyst (N.T.P.). After reaching thistemperature, so much air was fed into the system that the 0 content ofthe entrance gas passing into the reactora-mounted to 1-4%. The oxygenwas consumed in the combustion of the resin and carbon deposits whichblocked the catalyst, the excess of inert gas being carried out of thesystem. The addition of air was so controlled that the temperature inthe catalyst was kept in the vicinity of the hottest point at about 450to 550". After 36 hours the regeneration was completed since thetemperature peak had traversed the catalystlayer from top to bottom,essentially no more CO, formation was noted, and 0.3 to 0.6% of Oappeared in the exit gas fromthe reactor. v f

Thesystem was then'cooled to 350C. with the above mentioned inert gasmixture and filled with converted gas which contained 3% C0 and 48% Hand only 30 g./u'1. steam (N.T.P.). During the next three hours,

the catalyst was reduced by recycling converted gas therethrough at 350C., consumed gas being continually replaced by fresh gas.

The reactor was disconnected from the recycling system and againconnected to the conversion system and placed in operation using wetcrude gas at 23 atmospheres excess pressure.

The entering gas which contained 23.8% CO was con-- verted by theregenerated catalyst to a CO value of 2.5%;

, gas from hotcrude fuel gas high in carbon monoxide and attendantimpurities obtained by pressure gasification of solid carbon-containingfuels with steam and oxygen which comprises cooling said hot crude gasincluding unused steam therein to a temperature of from about to 200C.'under pressure to separate impurities such as high boilinghydrocarbon fractions, oils, tars and dust, removing said impuritiesfrom said crude gas and said unused steam, heating the cooled crude gasand said unused steam to a temperature between 250 and 400 C.,conducting the heated crude gas and said unused steam over a conversioncatalyst to convert the high carbon monoxide. content and steam unusedin the pressure gasification to carbon dioxide and hydrogensubstantially removing resin-formers and sulphur compounds duringsaidconversion, and thereafter recovering the purified lower carbonmonoxide contentrfuel gas.-

2. A process according to claim 1 wherein said cooling of the hot crudegas is carried out by injection of water thereinto, whereby the steamcontent of said crude gas is raised to an amount within the range offrom about 40 to 60% by volume. A

3. ,A process according to claim 1 wherein the hot crude gas to becooledis under pressure and the cooling, heating and converting stepsare carried out under the same pressure.

4. A process according to claim 1 wherein the. cooling, heating, andconverting steps are carried out under slightly lower pressure than thepressure of the starting hot crude gas.

5. A process according to claim 1 wherein the conversion catalyst is anactivated iron oxide catalyst.

' 6. A process according to claim 1 wherein the conversion catalyst isan iron oxide hydrate.

7. A process according to claim 1 wherein the conversion catalyst is anoxide of a metal of the 6th group of the periodic system of elements.

8. A process according to claim 1 wherein the conversion catalyst ismolybdenum oxide,

' 9. A process according to claim 1 wherein the conversioncatalyst istungsten oxide.

10. A process according to claim 1 wherein the conversion catalystcontains a metal ofthc 6th and' the 8th group of the periodic system ofelements.

11. A process .according to claim 1 wherein the conversion catalystcontains metal oxides of metals of the 6th and the 8th group of theperiodic system of elements.

12. A process according to claim 1 wherein'the conyersion catalyst iscobalt.

13. A process according to claim 1 wherein the con version catalyst isnickel with an oxide of the 6th group of the periodic system ofelements. 7 14. A process according to claim 1 wherein the heated crudegas and steam to be converted are conducted over catalyst containing anoxide of a metal of the 6th group of the periodic system of elements andthereafter over an iron oxide catalyst.

15. A process according to claim 1 wherein the catalvst is an iron oxideand the iron oxide, before contact with the crude gas and steam, ispretreated at 300 to 400 C. with already converted gas low in steamcontent.

16. A process according to claim 1 wherein the conversion catalyst maybe regenerated by treatment with an inert gas containing about '1 to 4%oxygen at from about 300 to 600 C., and thereafter effecting reductionby treatmeutwith already converted gas low in steam content.

' 17. A process according to claim 1 wherein the com version catalystmay be regenerated by treatment with steam containing about 1 to 4%oxygen at from about 300 to 600 C., and thereafter eifecting reductionby treatment with already converted gas low in steam content.

18. A process according to claim 1 wherein the but crude fuel gas to bepurified contains from about 20 to 25% carbon monoxide with respect todry gas.

19. A process for directly producing purified low carbon monoxidecontent fuel gas of density lower than cokeoven gas from hot crude fuelgas high in carbon monoxide and attendant impurities, said impuritiescomprising organic and inorganic sulfur compounds, ammonia, hydrogencyanide, resin-forming impurities, said fuel gas being obtained bypressure gasification of solid carboncontaining fuels with steam andoxygen, which comprises cooling the hot crude gas still under pressureand still containing unused steam in an amount of from 40 to 60%,obtained by pressure gasification, to a temperature of about 200 C. toseparate impurities such as high boiling hydrocarbon fractions, oils,tars, and dust, removing said impurities from said crude gas, heatingthe cooled crude gas still under pressure and still containing saidsteam to a temperature of at least 250 C., conducting the heated crudegas and said steam over a reducing catalyst whereby the carbon monoxidecontent and the containedsteam are substantially stoichiometricallyconverted to carbon dioxide and hydrogen substantially removingresinformers and sulfur compounds during said conversion, thereafterfurther cooling and scrubbing the converted gas and recovering thepurified lower carbon monoxide content fuel gas.

References Cited in the file of this patent UNITED STATES PATENTS

1.A PROCESS FOR DIRECTLY PRODUCING PURIFIED LOW CARBON MONOXIDE CONTENTFUEL GAS OF DENSITY LOWER THAN COKE-OVEN GAS FROM HOT CRUDE FUEL GASHIGH IN CARBON MONOXIDE AND ATTENDANT IMPURITIES OBTAINED BY PRESSUREGASIFICATION OF SOLID CARBON-CONTAINING FUELS WITH STEAM AND OXYGENWHICH COMPRISES COOLING SAID HOT CRUDE GAS INCLUDING UNUSED STEAMTHEREIN TO A TEMPERATURE OF FROM ABOUT 160 TO 2000*C. UNDER PRESSURE TOSEPARATE IMPURITIES SSUCH AS HIGH BOILING HYDROCARBON FRACTIONS, IOLSTARS AND DUST, REMOVING SAID IMPURITIES FOR SAID CRUDE GAS AND SAIDUNUSED STEAM, HEATING THE COOLED CRUDE GAS AND SAID UNUSED STEAM TO ATEMPERATURE BETWEEN 250 AND 400*C., CONDUCTING THE HEATED CRUDE GAS ANDSAID UNUSED STEAM OVER A CONVERSION CATALYST TO CONVERT THE HIGH CARBONMONOXIDE CONTENT AND STEAM UNUSED IN THE PRESSURE GASIFICATION TO CARBONDIOXIDE AND HYDROGEN SUBSTANTIALLY REMOVING RESIN-FORMERS AND SULPHURCOMPOUNDS DURING SAID CONVERSION, AND THEREAFTER RECOVERING THE PURIFIEDLOWER CARBON MONOXIDE CONTENT FUEL GAS.